Move unused forked code to external directory (#1192)

* Move unused forked code to external directory

* Fix SLN build errors

* Add back resource provider core since it's referenced by main resource provider project

* Update PackageProjects step of pipeline

external/Microsoft.SqlTools.Hosting.v2/ExtensibleServiceHost.cs

@@ -0,0 +1,59 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System.Collections.Generic;
+using Microsoft.SqlTools.Hosting.Channels;
+using Microsoft.SqlTools.Hosting.Extensibility;
+using Microsoft.SqlTools.Hosting.Utility;
+
+namespace Microsoft.SqlTools.Hosting
+{
+    public class ExtensibleServiceHost : ServiceHost
+    {
+        private readonly RegisteredServiceProvider serviceProvider;
+        
+        #region Construction
+
+        public ExtensibleServiceHost(RegisteredServiceProvider provider, ChannelBase protocolChannel)
+            : base(protocolChannel)
+        {
+            Validate.IsNotNull(nameof(provider), provider);
+            
+            provider.RegisterSingleService<IServiceHost>(this);
+            provider.RegisterHostedServices();
+            
+            // Initialize all hosted services
+            foreach (IHostedService service in provider.GetServices<IHostedService>())
+            {
+                service.InitializeService(this);
+            }
+
+            serviceProvider = provider;
+        }
+
+        /// <summary>
+        /// Constructs a new service host intended to be used as a JSON RPC server. StdIn is used
+        /// for receiving messages, StdOut is used for sending messages. Services will be
+        /// discovered from the assemblies in the current directory listed in 
+        /// <paramref name="assembliesToInclude"/>
+        /// </summary>
+        /// <param name="directory">Directory to include assemblies from</param>
+        /// <param name="assembliesToInclude">
+        /// List of assembly names in the current directory to search for service exports
+        /// </param>
+        /// <returns>Service host as a JSON RPC server over StdI/O</returns>
+        public static ExtensibleServiceHost CreateDefaultExtensibleServer(string directory, IList<string> assembliesToInclude)
+        {
+            Validate.IsNotNull(nameof(assembliesToInclude), assembliesToInclude);
+            
+            ExtensionServiceProvider serviceProvider = ExtensionServiceProvider.CreateFromAssembliesInDirectory(directory, assembliesToInclude);
+            return new ExtensibleServiceHost(serviceProvider, new StdioServerChannel());
+        }
+
+        #endregion
+
+        public IMultiServiceProvider ServiceProvider => serviceProvider;
+    }
+}